The present invention relates to blood flow measurement by thermodilution measurement, and more particularly to compensating for an injectate induced thermal effect on a thermal sensor in a retrograde catheter.
In native A-V fistulae, any stenosis is often located at the arterial portion of the vascular access or A-V shunt. The existence of a stenosis in the vascular access typically requires intervention to restore sufficient flow, or at least reduce the rate of occlusion. A typical interventional procedure is angioplasty.
The purpose of the interventional procedures, such as angioplasty, is to restore the flow through the vessel. Interventional radiologists and cardiologists therefore have a need to measure the efficacy of the flow restoring procedure.
In the angioplasty procedure, an interventional radiologist will insert a sheath (introducer) for the angioplasty balloon catheter facing the stenosis location and thus facing the blood flow in the vessel such as an A-V shunt. It is procedurally convenient to use the same introducer (sheath) for flow measurement. This procedure will locate the thermodilution catheter facing the blood flow and the position, facing the flow, is termed as xe2x80x9cretrogradexe2x80x9d position. Also in clinical situations such as angioplasty of extremities, it is convenient to reach the stenosis location from a downstream cannulation site. In all these situations, the thermodilution catheter will be facing the flow, and thus in a retrograde position. Yet, there remains a need for determining the blood flow rate.
Another situation is related to the endovascular procedure of placement of transjugular intrahepatic portosystemic shunts (TIPS). During the TIPS procedure, a special shunt is created to connect the portal vein with hepatic vein. The TIPS procedure is usually done to decrease the portal hypertension. However, the amount of blood that is taken by the shunt is unknown. If the amount of blood flow through the shunt is too high, then the amount of blood passing through the liver to be filtered is too small, which can result in damage to the patient. Alternatively, if the amount of blood flowing through the shunt and thus shunted from the liver, is small, then the effectiveness of the procedure is diminished. The need exists for determining the blood flow so that proper treatment can be administered.
Currently, blood flow measurements are performed not during intervention but later using color Doppler measurements of line velocity, but do not provide a blood flow measurement in ml/min.
Not withstanding, no practical, relatively quick, and low cost solution exists in the prior art for determining the relevant flow in these example procedures. Therefore, the need exists to measure blood flow using a catheter introduced into the vessel in retrograde direction. It is an object of the present invention to provide low cost flow measurement methods and devices for such measurements which solve the problems (and design constrains) of the retrograde thermodilution catheter.
The present invention is generally directed to determining blood flow rates, and more particularly to indicator dilution techniques, wherein a signal is introduced into the blood upstream and a downstream dilution signal is sensed. Of the indicator dilution methods, thermodilution is applicable in the present disclosure. In thermodilution measurements, an injectate (having a different temperature than the blood flow to be determined) is introduced at an upstream location and a thermal sensor (or dilution thermal sensor) monitors passage of the injectate at a downstream location.
In a number of configurations, a thermodilution catheter is employed, wherein the catheter includes an injectate lumen for introducing the injectate into the relevant blood stream and a dilution thermal sensor for monitoring a downstream passage of the injectate in the blood stream. The catheter can also include an injectate thermal sensor for providing a signal corresponding to an injectate temperature prior to introduction of the injectate into the blood flow.
As a consequence of thermal transfer, such as conduction or radiation within the catheter, the dilution thermal sensor in the retrograde catheter will register temperature changes, or effects, both by the injectate (indicator) passing through the catheter and the diluted blood flowing past the catheter. In this case, inside cooling of the dilution thermal sensor falsely increases the area under the resulting dilution curve and thus decreases the accuracy of the measurement.
The present invention also provides for measurement of the blood flow during the TIPS procedure, wherein the measurements can be conveniently performed by a retrograde catheter, introduced for example through the jugular vein, through the vena cava, and through the hepatic vein.
The measurements can be performed before intervention, after the shunt construction, in the shunt and in the vena porto (portacaval shunt). In this case, the retrograde catheter can be introduced through the hepatic vein, through the shunt and into the vena porta. The advantage of a blood flow measurement during the intervention is the ability to change the shunt flow if the shunt flow is not adequate.
The present configurations are directed to improving blood flow measurement accuracy in thermodilution measurements in a retrograde catheter by accounting for the presence of the inside cooling effect. The present configurations include (i) the pre-calibration of the thermal conductive properties of the catheter to determine Ki over an intended range of operating conditions, wherein the calibration data is used to adjust thermal measurements; (ii) a plurality of injections of different volumes or different time length from which a cooling effect on the dilution thermal sensor from inside the catheter can be determined, and/or an injectate temperature can be calculated; (iii) a plurality of thermal sensors, where the magnitude of the inside cooling effect on the dilution thermal sensor is measured by an additional thermal sensor and compensated; (iv) a plurality of pre-calibrated thermal sensors, to simultaneously eliminate the necessity of measuring the injectate temperature and the inside cooling effect; (v) creating special construction of the retrograde catheter to enhance, or maximize the thermal isolation of the injectate lumen from the dilution thermal sensor; or (vi) employing any combination of i-v.